Police have uncovered a million-dollar hydroponic cannabis growing operation inside an industrial unit at Wetherill Park on Friday, according to a police statement.

A man was charged after police conducted a search warrant at the premises and allegedly located 340 cannabis plants, with an estimated potential street value of $1 million, being cultivated in a sophisticated hydroponic set-up.

Police from Green Valley Local Area Command and the South West Metropolitan Region moved in property on Blackstone Street, Wetherill Park at about 8.40am.

Police seized the plants as well as equipment used to grow the cannabis, including heat lamps, filters, watering systems and electrical transformers.

During the search, police also seized loose cannabis head, cash and a smoke grenade.

A 61-year-old man, who police will allege was the leader of the syndicate, was arrested at the premises and taken to Green Valley Police Station.

The man was charged with large commercial cultivation of prohibited plant, use electricity without authority, supply of prohibited drug and dealing with the proceeds of crime.

He was refused bail to appear in Parramatta Local Court on Saturday.

The operation comes after investigations by police from Green Valley Local Area Command that had started in August 2013.

Four people have already been arrested and charged with a range of drug offences relating to an alleged cannabis-cultivation syndicate, according to an official police statement.

Between August 2013 and March 2014, police from Green Valley Local Area Command conducted investigations into the illegal cultivation and supply of cannabis in the area.